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Date: Mon, 14 Sep 2026 10:21:08 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Quentin Armitage <quentin@armitage.org.uk>
Cc: David Ahern <dsahern@kernel.org>, Ido Schimmel <idosch@nvidia.com>,
 netdev@vger.kernel.org
Subject: Re: net: parsing IFLA_INET_CONF broken since 7.1 if NLA_F_NESTED
 not set
Message-ID: <20260914102108.788e700f@kernel.org>
In-Reply-To: <49f5ad9f2a4c1f2178f64383b4f05c21106fce7b.camel@armitage.org.uk>
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On Mon, 14 Sep 2026 15:21:59 +0100 Quentin Armitage wrote:
> Commit fa8fca88714c - "ipv4: validate IPV4_DEVCONF attributes properly" changed
> inet_validate_link_af() to call nla_parse_nested() rather than
> nla_for_each_nested() for IFLA_INET_CONF. A side effect of this change is that
> the code now checks that NLA_F_NESTED is set for IFLA_INET_CONF, and rejects the
> message if it is not, whereas previously there was no check for NLA_F_NESTED
> being set.
> 
> The consequence of this is that code which worked prior to Linux 7.1, albeit
> erroneously not setting NLA_F_NESTED now fails.
> 
> In order to maintain backward compatibility, rather than calling
> nla_parse_nested(), nla_parse_nested_deprecated() should be called, as it is
> earlier in the function.

Please explain how you discovered the problem.
Is there some open source or closed source SW you're aware of which
breaks?